Sectional motor



v P. TROMBETTA SECTIONAL MOTOR Filed Jan. 14. 1925r wil Pan'i IO Trorn btte,

H is Attorney Patented Aug. 25, 1925.

UNITED STATES l 1,551,347 PATENT OFFICE..

. PANFILO TBOM'BETTA, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A. CORPORATION OF NEW YORK.

sEcrIoNaL Moron..

Application led January 14, 1924. Serial' No. 686,047.

To all whom t may concern:

Be it known-that I, PANFiLo TRoMBE'r'rA, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful ,Improvementsin Sectional Motors, of which the following is a speciication.

My invention rela-tes to a sectional electric motor. Although not limited thereto, my improved motor is particularly adapted to operate such apparatus as punch presses where a fly-wheel is utilized to store energy of rotation which energy is intermittently released to accomplish work through reciprocating apparatus.

The motor preferably utilizes the flywheel of the punch press or other apparatus as its rotor, and the stator which encloses a section only of the rotor, is prefer- "ably placed so as to magnetically carry the weight of the fly-wheel. Furthermore, I have' found that the characteristics of an al` ternating` current induction motor in which the secondary is a solid body of iron is cspecially suited for the direct driving of such apparatus.

The features of my invention which I believe to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention, reference is made in the following description to the accompanying drawings in which Fig. 1 illustrates the application of mymotor for driving the iiy-wheel of a punch press; and Fig. 2 represents the usual method of driving such apparatus and certain detrimental forces which my invention eliminates.

Referring first to Fig. 2, 10 indicates the iiy-wheel of a punch pressuof usual construction; 11 indicates the shaft which is driven by a pulley 12 and belt 13; 14 represents the die plunger which is reciprocated by the crank or eccentric 15; 16 and 17 represent bearings for shaft 11; 18 re resents the base against which the wor represented at 19, is held to be operated upon by the reciprocating member 14. The fly-wheel is necessary in this type of apparatus because the work done is all aecomplished at the instant the ldie 14 strikes the work 19.l The ily-wheel permits a. smaller and more uniform force than would otherwise be possible. It has heretofore been customary to drive the shaft 11 through a belt from a constant speed line shaft or an independently mounted constant speed motor allowing the slippage of the belt to ltake care 'of the fluctuation in the rotative speed of shaft 11 which is necessarily caused by the sudden application and removal of the load. In such cases the space required by the entire apparatus is considerable andthe fact that the driving motor or shaft and the punch press are not integral structures hlnders the tipping or turning of the punch press often necessary or desirable to get at a particular piece of work. The wear of the belt due to constant slipping re uires that it be renewed or repaired quite requently. The {1y-wheel is of considerable weight and produces a bending force on shaft 11 represented by the rarrow W. When the die plunger 14 strikes the work 19, a force represented by the arrow P is suddenly imposed on shaft 11 tending to bend itin the same direction around a oint falling in the bearing 16 between the y-wheel and eccentric 15. It is therefore evident that at the instant the stamping operation is accomplished, a heavy bending strain is imposed on the shaft 11 as well as on the bearings 16 and 17. It is therefore necessary to malte the shaf-t and bearings very rugged, but 1n spite of these precautions, the bearings must be renewed frequently since any great amount of wear in the bearings spoils the alinement of the reciprocating die 14 wlth respect to the base 18 and lessens the capacity of the machine to accompllsh accurate work. The application of my mvention to this t e of apparatus permits the elimination o theY detrimental force W, the pulley 12, the belt 13 and an external driving motor or shaft decreases the cost proportionally.

Referring now to `Fig.1, which representsv one application of myv invention, the general arrangement of fly-wheel 10, shaft 11, plunger 14 and base 18 are as usual. The

apparatus, instead of being driven indirectly', is driven directly b an electric motor,

the rotor of which is t e ily-wheel 10 and the stator of which is the primary member 20 of an induction motor which embraces the fly-wheel over av section only of lts periphery and preferably the upper section, in order that the inherent magnetic attraction between primary and. secondary may relieve the shaft 11 and bearing 16 from the weight of the {1y-wheel. This feature 'is generally applicable to all motors having cooperating stationary and rotating parts. v

I have found that a design of the motor suited for the other re uirements of this type of drive has `enoug magnetic attraction between rimary and secondar to slightly more than overcome the weig t of the required {1y-wheel. Vith such an arrangement, it will be eviden-t that the force W represented in Fig. 2 is eliminated and that the resultant force acting to bend the shaft 1p1 is greatly reduced. The strain on the bearings, particularly bearing 16, is also reduced permitting a less rugged construction of the shaft and bearings to he used or giving a longer useful life of such parts when of the usual construction.

Electricallythe stator 2O and its winding 21 are of usual construction and may be considered as being formed by cutting open a circular stator of usual construction and developing it into an arc of a circle, the radius of which is considerably O'reater than the original stator. The peripheral speed of the magnetic field produced by such a stator will be the same as before, but the actual speed in R. P. M. of the rotor of the increased radius will be reduced proportionately.

Owing to the circumferential interruption in the sectional stator, electricallosses occur at the ends of the stator which do not occur in the continuous stator but if the pole pitch is made small and the number of poles for the stator section is made comparatively large, such losses do not materially reduce the eiiiciency of the motor.

There are certain advantages other than those previously mentioned which the sectional motor has over the motor which is circumferentially complete. The theoretical speed in R. P. M. of the sectional motor may be made anything desired. To illustrate, the standard motor has a speed in R. P. M. which is fixed by the frequency of the source of supply and number of poles. 4 Thus, a 2-pole, 60 cycle standard motor has a synchronous speed of 3600 R. P. M. and the next possible lower speed is 1800 R. P. M. for a 4-pole motor, and if a speed of, say, 2400 R. P. M. is desired, it cannot be obtained directly. With the sectional motor, the theoretical speed in R. P. M. depends upon the frequency, the pole number and the arc of the rotor over which the sectional stator extends which of course may be made anything desired. So that, if a 60 cycle source is available and a speed of, say, 2400 R. P. M. is desired, it can be obtained directly by a 2-pole stator extending over 75 per cent of the rotor circum- I ference. The synchronous speed of the sectional motor may be expressed thus f 120 P R. M. P.= when It follows from what has been said that the capacity of the sectional motor may be materially changed by changing the percentage of the rotor periphery which it covers. Consequently, a great many different capacities may be had, all using a standard rotor, the number of poles and the circular arc of the stator being selected to give the desired speed in any case. The large mass of the fly-wheel serves as an efficient cooling means for the motor.

The standard induction motor, when designed for a very low angular speed, necessarily has many poles and a large diameter. Such a motor to have an efiiclent design, must be of suicient capacity to utilize the total periphery eliiciently. (Jonsequently, it is not practicable to build such a motor for small capacities. With the sectional motor on the other hand, a practicable small capacity low speed motor is` available, the capacity being determined by the peripheral length of the sectional stator. Furthermore, such a motor will have a peripheral speed large enough to make it a good induction motor.

As previously mentioned, the rotor of such a motor may constitute a ily-wheel having a solid periphery although in certain cases a squirrel cage rotor may be desirable. The use of an available fly-wheel as a rotor eliminates the usual rotor with its shaft and bearings, which is an important saving, not only in the cost of apparatus, but also in the space which it`occupies.

The characteristics of an induction motor with a solid iron or steel rotor are par.- ticularly suitable for the driving of punch presses, automatic hammers and such apparatus. Such a motor has very high starting torque, high slip, and'may be thrown directly on the line, as by means of the .switch 22 of Fig. l, without any starting compensator.

In order to illustrate practical design of such a motor, the following general specifications are given: For a S-phase source lof supply of 550 volts, 40 cycles, the following sectional motor requirements for a No. 21 Bliss punch press of 20 ton rating arel satisfactory for continuous operation at from 50 to 60 punches per minute; fly-wheel made of cast steel having a diameter of 36 inches with the other general dimensions proportioned as in Fig. l; the stator winding having 10 poles connected S-phase delta, proportioned to prevent overheating and covering 30% of the Icircumference of the fly-wheel;` the stator iron is laminated with 60 straight slots assembled in a cast iron yoke bolted to the punch press frame; air gap between stator and rotor .O6 inch.

Such a motor will have a starting current of about 10 amperes per phase and a running light current of approximately 25%' less. 'Ihe efficiency and power' factor of such a motor is appreciably lower than that of a standard induction motor with a squirrel cage rotor;` however, these disadvantages are more than offset by the other advantages previously mentioned. Being an induction motor of the solid steel rotor type, it is. capable of slipping without limit until it stops. This is highly desirable in case of punch presses where the stored energy of the fly-wheel is utilized to perform the punching, since the motor slip increases in order to allow the fly-wheel to do the punching. As stated above, the startingvcurrent is-very small and consequently such a motor can be thrown directly .on the line any number of times without injuring the motor. This feature is very convenient when setting dies since the fly-wheel may thus be turned by very small'amounts at a time by the motor instead of turning it by hand, as is the common practice.

In accordance with the provisions of the patent statutes7 I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof; but I desire to have it understood that the apparatus shown and described is only illustrative and that the invention may be carried out by other arrangements.

What I claim as new and desire to secure by Letters Patent of the United States, isf- 1. An alternating current induction motor having a rotatable secondary member and a stationary primary member, said members being concentrically arranged, said stator member having a uniformly distributed polyphase multipolar primary winding embracing only a portion of the periphery of said rotor and said rotor member constituting a solid body of magnetic material forming a iy-Wheel.

2. An electric motor comprising an armature mounted for rotation about a horizontally disposed axis and a cooperating stationary field member embracing only a portion of the periphery of said armature, said stationary member being so positioned with respect to said armature that the inherent magnetic attraction between them supports a substantial portion of the weight of said armature.

8. A rotary machine having a fly-Wheel, an induction motor for driving saidv machine comprising a sectional stator member provided with an induction motor primary winding and a cooperating secondary member, the latter constituting said fly-wheel, said stator member embracing only a portion of the periphery of said fly-wheel and positioned with respect theretoy so that the inherent magnetic attraction between the primary and secondary members substantially supports the weight of said fly-wheel.

4. A machine having a. horizontal rotatable shaft supported in bearings, an eccentric device on said shaft between the bearings for operating a vertical reciprocating part of said machine, a y-wheel ,on said shaft outside of one of the bearings, and means for driving said machine comprising an induction motor, the secondary and rotor of which constitute said ily-wheel and the primary of which constitute a. sectional stator supported on said machine above said fly-wheel.

In witness whereof, I have hereunto set my hand this 12th day of January, 1924'.

PANFILO TROMBETTA. i 

